'She had tantrums, slept badly and would line up her toys obsessively,' recalls Simone, 'but I just thought she had a strong personality. As she started to talk, she didn't use conversational language, but there were no other children around to compare her with so we didn't realise anything was wrong.

'But her behaviour deteriorated as she got older,' Simone says. 'Eventually, she would be awake for seven hours a night. She was very much in her own world, and wasn't interested in other people.

Blood and urine tests suggested Sienna's gut was indeed inflamed, and she was placed on a gluten and dairy-free diet. 'Within a couple of days, Sienna said "water" and pointed to the tap - something she'd never done before,' says her mother. Though they cannot prove this was linked to a change in diet, it seemed more than coincidence.

The next step was a 'specific carbohydrate diet' - a regime avoiding complex carbohydrates such as bread, cereal and pasta to rid the gut of harmful bacteria and reduce inflammation. [boldface added]

Her behaviour improved within days of the special diet. [boldface not added]